<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>4-可选链操作符</title>
</head>
<body>
    <script>
        // ?.
        function main (config) {
            // const dbHost = config && config.db && config.db.host;
            const dbHost = config?.db?.host;
            console.log(dbHost);
        }

        main({
            db: {
                host: `192.168.1.100`,
                username: `root`
            },
            cache: {
                host: `192.168.1.200`,
                username: `admin`
            }
        })
    </script>
</body>
</html>